Drugs that are weak bases will be present in breast milk at the same or higher concentrations than in plasma. Conversely, drugs that are weak acids will be present in breast milk at a much lower concentration than in the plasma.

To increase excretion: change the urinary pH to favor the charged form of the drug: Weak acids: excreted faster in alkaline pH (anion form favored) Weak bases: excreted faster in acidic pH (cation form favored)